1. Field of the Invention
This invention relates to a method of producing an iron-, cobalt-, or nickel-base alloy of high purity, and more particularly to a method of producing an alloy containing at least one major ingredient selected from the group consisting of iron (Fe), cobalt (Co), and nickel (Ni) and having low contents of sulphur, oxygen, and nitrogen.
2. Related Art Statement
As already known, an iron-, cobalt- or nickel-base alloy is excellent in mechanical property, thermal resistance and corrosion resistance. When residual oxygen and sulphur are excessive, however, the alloy is deteriorated in workability. Therefore, it is important to sufficiently decrease residual oxygen and sulphur.
In general, it has been well-known that calcia (CaO) refractories is stable even at high temperature and used for melting each kind of alloys having high reactivity. When aluminum (Al) or aluminum alloy is added to a molten bath in a vessel or ladle lined with this calcia (CaO) refractory, it has also been well-known that calcia (CaO) is reduced by aluminum (Al) to produce metallic calcium (Ca), and deoxidation and desulfurization is proceeded by said calcium (Ca).
That is, Japanese Patent Publication Nos. 849/79, 24,688/79 (Japanese Patent No. 992,541), and 25,486/85 describe a method of deoxidizing and desulphurizing molten steel by adding aluminum or an aluminum alloy to the molten steel in vacuum or in an argon atmosphere with the use of a melting furnace, a crucible or a ladle lined with a basic refractories having high contents of CaO. The essence of this method is to reduce calcium (CaO) in the lined refractories by adding aluminum (Al) and to remove sulphur and oxygen in the molten steel by calcia (Ca) as a reduced product. U.S. Pat. No. 4,484,946 further describes a method of deoxidizing and desulphurizing molten steel, in case of repeatedly using a melting furnace or a crucible lined with said based refractories, wherein as oxysulfide of calcium is accumulated on a wall surface of the melting furnace or the crucible and a deoxidizing rate or a desulphurizing rate of the iron alloy is reduced, an additive such as aluminum together with or without flux is added to the molten steel, thereby preventing said compound from accumulating on the wall surface of the melting furnace, the ladle or the crucible.
According to the above method, it is possible to reduce sulphur in the molten steel to about 0.004% by weight and oxygen in the molten steel to 0.002% by weight. However, it is expected to find a more super refining technique having more higher desulphurization and more deoxidation in the field of refining alloys.